(1) Continuation of studies on the bicyclic cascade regulation of glutamine synthetase, involving the development of an improved purification procedure for the uridylytransferase (UT) and uridylyl-removing (UR) enzyme. Hydrophobic column chromatography on phenyl-sepharose was added. We have shown that a single polypeptide is responsbile for both UT and UR activities. HPLC analysis indicated that UT-UR enzymes exists as a mixture of various oligomers and that both VT-VR activities are due to the monomeric form. Molecular weight of monomer evaluated by HPLC was 92,000-94,000. Amino acid composition of UT-UR was also determined. (2) Preparation of monoclonal antibodies specific to AMP moiety of adenylylated glutamine synthetase is in progress. BALB/C mice were immunized with BSA-AMP and antibody producing B lymphocytes were fused with myeloma cells. (3) A photoactive analog of ATP, 8-azido ATP was synthesized. Specific photolabeling of the active site of glutamine synthetase has been attempted without success.